In electromagnetism, there are two kinds of dipoles:
An electric dipole deals with the separation of the positive and negative charges found in any electromagnetic system. A simple example of this system is a pair of electric charges of equal magnitude but opposite sign separated by some typically small distance. (A permanent electric dipole is called an electret.)
A magnetic dipole is the closed circulation of an electric current system. A simple example is a single loop of wire with constant current through it. A bar magnet is an example of a magnet with a permanent magnetic dipole moment.Dipoles, whether electric or magnetic, can be characterized by their dipole moment, a vector quantity. For the simple electric dipole, the electric dipole moment points from the negative charge towards the positive charge, and has a magnitude equal to the strength of each charge times the separation between the charges. (To be precise: for the definition of the dipole moment, one should always consider the "dipole limit", where, for example, the distance of the generating charges should converge to 0 while simultaneously, the charge strength should diverge to infinity in such a way that the product remains a positive constant.)
For the magnetic (dipole) current loop, the magnetic dipole moment points through the loop (according to the right hand grip rule), with a magnitude equal to the current in the loop times the area of the loop.
Similar to magnetic current loops, the electron particle and some other fundamental particles have magnetic dipole moments, as an electron generates a magnetic field identical to that generated by a very small current loop. However, an electron's magnetic dipole moment is not due to a current loop, but to an intrinsic property of the electron. The electron may also have an electric dipole moment though such has yet to be observed (see electron electric dipole moment).
A permanent magnet, such as a bar magnet, owes its magnetism to the intrinsic magnetic dipole moment of the electron. The two ends of a bar magnet are referred to as poles—not to be confused with monopoles, see Classification below)—and may be labeled "north" and "south". In terms of the Earth's magnetic field, they are respectively "north-seeking" and "south-seeking" poles: if the magnet were freely suspended in the Earth's magnetic field, the north-seeking pole would point towards the north and the south-seeking pole would point towards the south. The dipole moment of the bar magnet points from its magnetic south to its magnetic north pole. In a magnetic compass, the north pole of a bar magnet points north. However, that means that Earth's geomagnetic north pole is the south pole (south-seeking pole) of its dipole moment and vice versa.
The only known mechanisms for the creation of magnetic dipoles are by current loops or quantum-mechanical spin since the existence of magnetic monopoles has never been experimentally demonstrated.
The term comes from the Greek δίς (dis), "twice" and πόλος (polos), "axis".
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Ok I have a contradiction in my mind:
Patch antenna is called a leaky wave resonant cavity because of the magnetic slots which radiates. We all agree on the fact that they are standing waves with clearly identified max and min as a characteristic of a specific mode inside this cavity...
I cannot find the answer to my question anywhere on the internet so hopefully someone here will end my long search with the correct answer.
It is well known that a single water molecule has a permanent electric dipole which produces a dipole intrinsic electric field. Let's say the dipole is...
Homework Statement
A Hertzian dipole is short compared with the wavelength of the radiation it emits. It describes ’short’ radio antennas and the scattering of electromagnetic radiation by small particles.
(a) Give an upper limit for the length of a Hertzian dipole antenna operating at 300 kHz...
Firstly apologies for not typing this out - but I need the diagram. And I have no idea where to start. I 'think' most of it is correct. BUT - I have no idea what to do with the last part of c. I thought I could just double the energy. But I'm going to get a negative energy for the system...
Homework Statement
The Earth's magnetic field is essentially that of a magnetic dipole. If the field near the North Pole is about 10^-4 T, what will it be (approximately) 13,000 km above the surface at the North Pole?
Homework Equations
B = \frac{\mu _0}{2\pi}\frac{\mu}{(R^2+x^2)^{3/2}}
for...
Hello everyone,
I would like to ask a couple of questions which are related to electric dipole moment and electric field.
First one: Let us assume that we have somehow a constant electric field. The obvious thing to say is that any material that contains a Net Charge ( moving one or not moving...
I am confused with the classical approach of usage of a "transition dipole oscillation" in order to explain the broadening of spectrum of emission between energy levels.
1. If I understand it correctly then emission of photon is due to oscillation of a dipole consisting of an electron-proton...
Hello Everyone,
Kindly, may anyone please tell me what are the allowed and forbidden transition dipole moments between different molecular electronic states in diatomic molecules?
Thank you so much in advance...
Homework Statement
Show that the energy of an ideal dipole p in an electric field E is given by
U = -p ⋅ E
Homework Equations
Work = θτ where τ is torque
τ = p × E
The Attempt at a Solution
U = ∫(p × E) dθ' (from θ to 0, since the dipole will eventually align itself with the magnetic...
Hey there,
The basic unit for magnetic dipoles is the bohr magneton
μB = e ħ / 2 me
Is it possible to have a magnetic dipole moment of a fraction of a bohr magneton, say, 0.5 μB
Is it possible because the mp of a proton is greater than that of an electron, so following the same formula, its...
Hello,
I am reading the volume 2 of the Feynman's Lectures on Physics, and something is bothering me when he calculates the dipole moment of a single atom induced by an extern field ...
Hello,
I am reading the volume 2 of the Feynman's Lectures on Physics, and something is bothering me when he calculates the dipole moment of a single atom induced by an extern field ...
Some literatures say that the selection rule in electric dipole approx. for angular momentum ##\Delta j = 0,-1,1## some other say ##\Delta l = -1,1##. I follow the notation used in my references, despite the difference I think since j and l are both angular momenta which fulfill angular momentum...
I have come up with a paradox: Ionic crystals, in which cations and anions form a lattice, seems to have total electric dipole moment!
For example, consider a one dimensional example:
##+ - + - + - ... + - + -##
In the above picture, a ##+## represents a cation and a ##-## represents an anion...
Homework Statement
Show that: ##B=\frac { 1 }{ 4\pi \epsilon r^{ 3 } } \left[ 3\hat { r } \left( \hat { r } \cdot \vec { m } \right) -\vec { m } \right] ##
Homework Equations
B=delxA, m=a*I
The Attempt at a Solution
[/B]
I follow my professors derivation. However, she expands the term...
Hello Everyone,
A little question regarding the TDMs between two different electronic states of a diatomic molecule. If I am calculating the TDM from state A to state B, is it the same if we are calculating the TDM from state B to state A? Are these two transitions the same?
Thank you so much...
For an EM wave close to the transition frequency ##\omega_{21}##, we assume the dipole moment to be exponentially damped and oscillating:
p(t) = p(0) e^{-\frac{\gamma}{2}t} cos(\omega_0 t)
Why do we expect the electric field to be proportional to ##\dot p##?
Taken from my lecturer notes on...
Alright so I am building a few half wavelength dipole antennas for a project and was wondering how large the space should be between each side of the dipole antenna. I have asked a radio forum and they could not help me so I came here. Thanks.
Also I herd that an 1 and a half wavelength...
Homework Statement
Select all of the following which are possible combinations of Lz and θ for hydrogen atoms in a d state, where Lz is the z component of the angular momentum L, and θ is the angle between the +zaxis and the magnetic dipole moment µℓ due to the electron's orbital motion...
Homework Statement
A dipole is centered at the origin, and is composed of charged particles with charge +e and -e, separated by a distance 9 ✕ 10-10 m along the y axis. The +e charge is on the -y axis, and the -echarge is on the +y axis.
An electron is located at <-3 ✕ 10^-8, 0, 0> m. What is...
A negative charge cloud distribute as a ellipsoid and a positive point charge situated at the centre of the ellipsoid.What should be the dipole moment of charge distribution.I mean, if the negative charge distribution is spherical and positive point charge at the centre then surely dipole moment...
Homework Statement
Hi everyone,
My problem is fairly simple: We have a circular current loop enclosing area A, and with a constant current I. The loop is rotating about its diameter at a constant angular frequency \omega. All we need to do is find the electric dipole, and magnetic dipole...
For a dipole, if there is point subtending an angle ##\theta## at the centre of dipole and at a distance ##r## from centre of dipole, then the electric field at that point can be broken into 2 components. One along the line joining the point and centre of dipole and point given by...
When making an extension from linear dipole antennas to small circular antennas, I am only coming across expressions for a magnetic dipole moment (as opposed to having just an electric dipole moment for a linear dipole antenna). The expression being:
m = πr2I at its peak
The above expression...
Today, I made the following question at Physics SE, but the community redirected me here
In short, I have made a proof for EF/MF phase difference near an oscilating dipole that "vanishes" far away from the dipole. So, what I am asking for is a proof verification.
The physics SE post...
Imagine an electric dipole with charges ##+q##, ##-q##, mass ##m## and size ##d##.
Assume this dipole is oriented horizontally and is sitting at rest on top of some weighing scales on earth.
As the charges are at rest the weight of the dipole is just ##-mg##.
But by the principle of...
Homework Statement
Text description: Let V(z) be the potential of a ring of charge on the axis of symmetry at
distance z from the center. Obtain the first two non-vanishing terms of the multipole expansion
for V(z) with z>>a where a is the radius of the ring. Can you see by symmetry that the...
Homework Statement
Show that the force on an elementary dipole of moment ##\mathbf{p}##, distance ##\mathbf{r}## from a point charge ##q## has components
$$\begin{eqnarray}
F_r &=& -\frac{qp\cos{\theta}}{2\pi\epsilon_0 r^3}\\
F_\theta &=& -\frac{qp\sin{\theta}}{4\pi\epsilon_0 r^3}...
Don't kill me, but I have a problem understanding and answering a question of what it means to be moving towards/away from CMB rest frame.
The CMB is a sphere around earth, and corresponds to the last scattering surface of the Universe. If we are moving with respect to it, doesn't that mean we...
Homework Statement
An electric dipole consists of two charges of equal magnitude ##q## and opposite sign, which are kept at a distance ##d## apart. The dipole moment is ##p= qd## .
Let us next place two such dipoles, placed at distance ##r## apart, as shown in the accompanying figure.
a)...
It is known that the dipole anisotropies of the CMB radiation, can give the relative velocity of the Earth with respect to the CMB "rest" frame...
In first order, this is given by \beta \approx 1.2 \times 10^{-3} or u_{CMB} \approx 360 km/s .
I have one question here:
Why is the velocity given...
Homework Statement
Why isn't the expression for torque on a dipole kept in an external electric field ExP? Why is it PxE?
No such indication has been given in any of the derivations, that it is mandatory for it to be PxE, so why can't it be ExP?
2. The attempt at a solution
Is it all about...
Homework Statement
Consider an ideal stationary magnetic dipole ##\vec{m}## in a static electric field ##\vec{E}##. Show that the fields carry momentum ##\vec{p} = -\epsilon_0\mu_0\left(\vec{m}\times\vec{E}\right)##.
Homework Equations
Momentum stored in electromagnetic fields: ##\vec{p} =...
Homework Statement
The problem is to show that the potential energy of a dipole (whether electric or magnetic) is given by ##U = -\vec{m}\cdot\vec{B}## in the magnetic case and ##U = -\vec{p}\cdot\vec{E}## in the electric case assuming the respective magnitudes of the dipole moment remain...
edit: The title is misleading, sorry. Originally I wanted to ask a question about the heat capacity but I figured it out and changed the question while forgetting to change the thread title..
Hi. OK, assume we have a classic magnetic dipole in a magnetic field with ##H= - \vec{\mu} \cdot...
Can someone explain how to determine if a compound has a dipole moment and how to determine how big or small it is (possibly numerical value)? I have a final tomorrow and I've looked this up on multiple website and cannot find any good explanation.
Homework Statement
Suppose a radiating electric dipole lies along the z axis. Let ##I_1## be the intensity of the radiation at a distance of 10 m and an angle of 90 degrees. Find the intensity (in terms of ##I_1##) at (a) a distance of 30 m and an angle of 90 degrees, (b) a distance of 10 m...
The problem is as follows: There is a point magnetic dipole embedded at the center of a sphere (radius R) of linear magnetic material of permeability μ. What is the magnetic field inside the sphere?
I know that this problem has been solved in many books.But I am trying a different method. Since...
Why does hydroquinone possesses non zero dipole moment? The OH groups present at para positions on the benzene ring should cancel the effect of each other...if there is a plane change then exactly in which cases molecules do change planes?
Hello there,
I want to derive ##U(\theta) ## for electric dipole placed in uniforum electric field $\vec{E} = E\vec{e}_x$ where E is constant. I define the dipole moment as $p = qd$, where $d$ is the distance from the two
I write $\mathm{d}W = p\,E\sin\theta \mathrm{d}\theta =...
Homework Statement
Hi, I've been having problems visualizing and interpreting a situation where there is zero potential in a point, equidistant, between two opposite charges. What is the significance of this? Here's a sample problem:Consider two point charges. One has a charge of +1 μC and the...
Homework Statement
[problem 3.49 from Griffiths' Introduction to Electrodynamics 4th edition. The relevant equations from the book are reproduced in "relevant equations" below] In Ex. 3.9, we obtained the potential of a spherical shell with surface charge ##\sigma(\theta) = k\cos\theta##. In...
Homework Statement
For a fixed given electrical power to two monopole sources, producing the same frequency. Which mode, either in-phase or out of phase, will radiate the most sound power into the far-field?
Homework Equations
Is the radiated sound power dependant of the given electrical...
Homework Statement
I am trying to calculate the dipole moment of a cylinder of volume charge density ##\rho_0## of radius ##R## and height ##H## with is center coinciding with the origin. My guess is that it should be 0 because of the symmetry but I am not able to show it. Below is my...
Hi all,
I am reading a book on atom interaction with light. It starts with the 2 level system. The book said the diagonal elements of dipole operator is zero, i.e. ##\langle g|x|g\rangle = \langle e|x|e\rangle = 0##. I don't understand why this is true but after searching online and there...
Hi,
I wasn't sure if this is more Physics/Astro or chemistry because its actually all 3.
i've got some conceptual issues with some tasks at hands, and was wondering if anyone could clear that up for me.
(These questions are all regarding molecules)
1) How do you create a potential energy...
Homework Statement
A magnetic dipole m is moved from infinitely far away to a point on the axis of a fixed, perfectly conducting (zero resistance) circular loop of radius a and self-inductance L. In its final position the dipole is oriented along the axis of the loop and is a distance z from...
Homework Statement
Suppose a grounded spherical conducting shell of radius R surrounds a pointlike dipole at the center with \vec{p}=p\vec{k} Find the potential V(r,\theta) for r <= R. Hint: Use spherical harmonics regular at r=0 to satisfy the boundary condition.
Homework Equations
General...